1. Field of Invention
The present invention relates to a method and control system for controlling pasteurization of food products.
2. Background
In food products, heating can bring both benefits and detriments to the products. For example, heating can pasteurize, tenderize and/or cook food products. Too much or too poorly controlled heating, on the other hand, can impair the functionality of and, e.g., cook or significantly alter the flavor profiles of food products that are supposed to be uncooked (i.e., that are supposed to substantially retain the useful properties of the uncooked product), or, e.g., toughen, burn, dessicate or significantly alter the flavor profiles of cooked food products.
Pasteurizing of proteinaceous food product can be carried out by heating to destroy infectious organisms such as salmonella. Pasteurization may be defined as heat treatment for the purpose of killing or inactivating disease-causing organisms. For example for milk, a minimum exposure for pasteurization is 62xc2x0 C. for 30 minutes or 72xc2x0 C. for 15 seconds. The latter exposure is called flash pasteurization. Complete sterilization may require ultra-high pasteurization such as treatment at 94xc2x0 C. for 3 seconds to 150xc2x0 C. for 1 second to kill pathogenic bacteria and inactivate enzymes that cause deterioration and to provide for satisfactory storage life.
Minimum food safety processing standards for various commodities have been promulgated and are enforced by the United States Department of Agriculture (USDA). Pasteurization may be defined in accord with the standards mandated by the USDA. The Nutrition Action Health Letter published by the Center For Science In The Public Interest (July/August 1991 Edition, Vol. 18, No. 6, xe2x80x9cName Your (Food) Poisonxe2x80x9d) describes concern with the growing number of cases of food poisoning due to food infections.
Many known processes for pasteurizing food are insufficient to assure safety of some foods from infections or cannot be applied to some food products. The xe2x80x9cName Your (Food) Poisonxe2x80x9d article reports that dairy products, eggs, poultry, red meat and seafood, in that order, are the most common causes of food poisoning. Shell eggs are particularly difficult to pasteurize because of their structure. The article indicates that one of 10,000 eggs is contaminated with salmonella enteritis.
The United States Department of Agriculture (USDA) regulates minimum safety standards for pasteurizing in-shell eggs. These standards are promulgated in order to ensure that certain microorganisms, including such infectious organisms as Salmonella, are substantially destroyed prior to distribution and consumption of the eggs. The USDA defines pasteurization as a heat treatment for the purpose of killing these disease-causing organisms.
One source of infection arises when the egg shells come into contact with organic refuse. Contamination results because the egg shells have numerous pores which permit infectious microbes, which are contained in the organic refuse, to penetrate the pores of the eggs. Another source of infection results from trans-ovarian contamination. This occurs when chickens or other poultry ingest or are otherwise infected by infectious microbes and transfer the microorganisms directly into the eggs.
Techniques for improving pasteurization of eggs have been proposed. These techniques attempt to destroy infectious disease causing organisms in in-shell eggs without substantial loss of functionality. One approach to pasteurizing in-shell eggs involves heating the in-shell eggs in water baths, for various times and at various temperatures. The time/temperature ratios vary widely because different approaches involve a compromise between the degree of safety achieved and the quality or the functionality of the eggs retained after pasteurization is completed. The USDA has devised time/temperature ratios, but they are only for liquid eggs.
Cox et al. (PCT/US94/12950), which is hereby incorporated by reference, discloses a method for destroying infectious disease causing organisms in in-shell eggs without substantial loss of functionality. Cox et al. employs a temperature versus time relationship in order to accomplish pasteurization of the in-shell eggs. An initial egg temperature and processing temperature at the beginning of the pasteurizing process of a whole shell egg must be known. These temperatures are used to determine the total processing time, e.g., the total length of time over which the eggs are heated. According to a preferred embodiment of Cox et al., minimum temperatures/time requirements for liquid whole eggs are applied equivalently to in-shell eggs once the selected pasteurization temperature has been achieved at the shell egg yolk center.
Cox et al. uses the following temperature timetable for determining the pasteurization time of in-shell eggs.
This table describes the processing of in-shell eggs after they attain the required pasteurizing preprocessing temperature. The initial temperature is applied until the in-shell eggs reach a temperature equilibrium with the heat transfer medium. The RPT for a given pasteurization regimen can only begin after this point has been reached.
Cox et al. also discloses that factors including the size and internal initial temperature of the eggs may affect the time required for the eggs to reach the effective processing temperature. Thus, an initial temperature that causes pasteurization of one batch of eggs may result in impaired functionality of a second batch of eggs having a smaller size, depending on the variables associated with that particular batch of eggs.
Davidson International Application No. PCTI/US96/13006 (U.S. application Ser. No. 08/519,184), also discloses methods to pasteurize in-shell eggs using time/temperature relationships. In particular, Davidson discloses heating a yolk of the egg to within the range of 128xc2x0 F. to 138.5xc2x0 F. Once the yolk reaches this temperature range, it must be maintained at this temperature range for a certain time and within certain parameters.
FIG. 1 shows a temperature versus time curve implemented by the Davidson system. This curve is based substantially on the data of the above table. Referring to FIG. 1, the temperature of the egg yolk must be maintained between parameter line A and parameter line B in order for sufficient pasteurization to occur. According to Davidson, this will reduce the Salmonella by at least 5 logs, while at the same time retaining the functionality of the eggs. If the eggs are heated to a limit outside parameter lines A and B, however, the eggs will either lose their functionality or remain insufficiently pasteurized. Thus, according to Davidson it is imperative that the temperature of this system should stay within the predefined parameters.
Factors such as loss of water, temperature overshoot (e.g., raising the temperature too high), inefficient temperature sensors (e.g., low response time for raising the temperature to a predefined temperature range), and numerous other factors make it possible for the bath temperature to stray from preferred parameters. The size of the eggs, the number of eggs placed in the bath and the initial internal temperature of the eggs will also affect the pasteurization time and functionality of the eggs.
Whole eggs are not the only food products that are subject to bacterial or other such contamination. For example, other uncooked proteinaceous food products such as uncooked meat (e.g., beef, veal, pork, mutton, lamb or poultry), fin fish and shellfish (e.g., oysters, clams, scallops, mussels, crabs) are all too often contaminated with bacteria such as E. coli and others. The contamination may occur in nature or during processing. An especially common source of contamination exists in processing facilities, where surfaces of large quantities of food products are exposed to cutting, penetrating and transporting equipment that may bear contaminants. Especially in ground or sliced products such as ground meat and seafood, the contamination can be spread throughout a large volume of the product.
Such contamination is not limited to uncooked products. Many food products today are partially or fully pre-cooked and then stored and/or transported under ambient, refrigerated and/or frozen conditions before or after sale. Food products are also commonly subjected to post-cooking processing; e.g., slicing (as with bologna, pepperoni, and other packaged meat or fish slices), mixing (as with xe2x80x9csaladsxe2x80x9d such as egg salad, seafood salad, tuna salad, ham salad, and xe2x80x9cdevilledxe2x80x9d products such as devilled ham), packaging, etc. where bacterial contamination and the like can be introduced into or onto the product.
Contamination is also not limited to proteinaceous food products. For example, non-proteinaceous food products such as fruits, fruit juices and vegetables have been found to be contaminated with bacteria including E. coli. Such other foods are also subject to natural and pre- and post-cooking processing conditions in which hazardous contamination can occur.
Efforts have been made to pasteurize cooked food products. However, such efforts have tended to focus on high temperature treatments or irradiation, which can pasteurize the surface of the product, but can cause adverse effects on the functionality of the product if an attempt were made to pasteurize the entire volume of the product. Surface pasteurization may be unacceptable with many cooked products, especially those that have been ground, sliced, mixed or otherwise had their interiors exposed to potential contamination after cooking (or before cooking where the cooking was not so thorough as to kill microorganisms in the interior of the product).
In my U.S. Pat. No. 5,916,617, the entire contents of which are hereby incorporated by reference, I describe processes for heat treatment of proteinaceous food products. Such processes involve heating the products at controlled temperatures and can, for example pasteurize the products without substantially impairing their functionality.
As discussed above with respect to egg pasteurization, many factors can cause heating temperatures to stray from preferred parameters. A result can be that, even when heat treated within or near a temperature range considered acceptable, variations can occur among products treated for the same length of time. Such variation itself, as well as properties of the product resulting from such variation, may be very harmful to food products.
Functionality is defined herein as the capability of a food product to provide the properties of the product that has not been treated by the process of the present invention. Loss of functionality is determined by observing the loss of quality of the food product. See my U.S. Pat. No. 5,916,617. For example, spoilage or cooking is a loss of functionality of meat in a process designed for aging of meat without cooking. Coagulation is a loss of functionality of shell eggs during pasteurization. Cooking, loss of taste and loss of texture are each a loss of functionality of oysters that are to be eaten uncooked. Overcooking such as burning or toughening, or even overcooking beyond the pre-pasteurization condition (e.g., from rare to medium or well done), or dessicating is a loss of functionality for cooked products.
The extent to which functional properties of a food product are affected by heating may be determined by testing the performance of the product under conditions in which the damage is readily observed. For example, functionality of eggs can be established by determining the quality of food products that depend upon the quality of coagulation of the egg. Such food products may include custards and pie fillings and loaves or croquettes, which depend upon the binding of food together that may be provided by the quality of egg coagulation. The functional properties may also include the elasticity of an egg protein film or the emulsifying ability to disperse oil in the making of mayonnaise and salad dressings. Functionality or functional properties of other food product are similarly established in terms of the capability of the food product to perform intended purposes after heat treatment including retaining a xe2x80x9cnaturalxe2x80x9d taste and texture.
The present invention comprises a method and control system for controlling pasteurization of food products, preferably in a heated fluid.
In embodiments of methods and control systems of the present invention, a value of a desired pasteurization property of the product is achieved by heat treatment. The temperature of the product is periodically or continuously determined. A rate of change of the desired pasteurization property based on the temperature of the product is also periodically or continuously determined.
A cumulative value of the pasteurization property change as a function of the rate of change and time is also periodically or continuously determined. The cumulative value is periodically or continuously compared to at least one predetermined value. A signal is generated when a predetermined relationship between the cumulative value and the predetermined value is revealed. The time at which comparing takes place may be before, at and/or after a predetermined time at which sufficient pasteurization is expected to be completed.
In embodiments, the invention also provides methods of pasteurizing cooked food products, in which cooked food is subjected to heat treatment at a temperature above a minimum pasteurization temperature, but below an acceptable cooked temperature of the product. Thus for instance, the cooked food is subjected to a temperature below but near, for instance within 5 or 10xc2x0 F. below, a minimum temperature at which it was cooked, whereby pasteurization is achieved without further cooking.
The invention is particularly useful for, although not limited to, pasteurization of proteinaceous food product. While heat treatment may be effective in pasteurizing proteinaceous food product, heating at the same time may destroy some functionality or functional properties of the product. For example, it can partially cook an uncooked product or overcook a pre-cooked product. The present invention provides a process for pasteurizing proteinaceous food product that can achieve a delicate balancing of effective pasteurization without substantial destruction of functionality or functional properties.